Method for reducing data loss in automatically re-configured ATM networks

ABSTRACT

In an ATM network, data loss caused by pre-programmed network optimizations can be reduced or avoided if a record of such optimizations is made, and if, prior to another optimization, some event occurs. The detection of some external event should indicate that another optimization is warranted.

FIELD OF THE INVENTION

This invention relates to asynchronous transfer mode (ATM) datanetworks. In particular, this invention relates to ATM data networkshaving so-called permanent virtual circuit (PVC) data paths that areautomatically re-configured in an attempt to maximize network efficiencyand capacity.

BACKGROUND OF THE INVENTION

ATM-format data and ATM networks are well known in the data andcommunications art. Briefly, in an ATM network, data is routed from asource to a destination over a path that is comprised of one or more ATMswitches. An ATM switch receives ATM data packets on an incoming port orterminal and routes the ATM data packets out on an outgoing port orterminal. The outgoing port of one ATM switch is frequently coupled toan input port of another ATM switch. Eventually, the data is routedthrough the switches of an ATM network to its destination where it is tobe used.

Most ATM networks include numerous ATM switches, each receiving incomingdata packets and routing data to some other switch in the network. As iswell known in the art, the several switches of an ATM network receivedata packets that are addressed to only the next ATM switch thatcomprise the path over which data is sent from a source to adestination.

Virtually all ATM switches are software controlled, allowing forincreased functionality, among other things. At least one feature of asoftware-based ATM switch is the ability to set up and tear downconnections through the actual switching fabric through which datapasses between a switch input port and a switch output port. The abilityto specify a path through the switch enables the ATM to route data alongits way to a destination.

In an ATM network, at least one type of path is a so-called permanentvirtual circuit or PVC which is a path through the network that istypically set up once. Setting up a PVC requires that each of the ATMswitches through which data is to be routed, be programmed to connectincoming data on a particular transmission media onto a particularoutgoing data port by which the data can be delivered to itsdestination. Unlike a so-called switched virtual circuit or SVC by whicha data path through an ATM network can change during the course of acall, a PVC is a relatively long-life path through an ATM network.

Many ATM network operators monitor the traffic loading on the PVCs intheir networks so as to adjust the data paths through the network tomaximize network efficiency. In fact, many ATM switches arepre-programmed to continuously optimize data capacity through thenetwork by re-routing a customer's data from one PVC to another PVC. Insome instances, the PVC over which a customer's data is carried is torndown after the data stream is routed onto another PVC. Re-routing dataalmost always causes at least some data loss.

Optimizing network capacity frequently requires that a data stream (thedata transferred between a source and destination or the data of aparticular customer of the ATM network provider) is re-routed throughthe network for network reliability or to maintain network capacity orfor other reasons. Notwithstanding the fact that ATM switches arecomputer controlled and the switching software and switching hardwareoperates at what many consider to be blinding speed, rerouting datathrough PVCs in an ATM network in pursuit of network optimization almostalways causes some of the data of a data stream to be lost. This alsoimpacts system real time by requiring the system to change routes.

Data loss caused by automatic path optimization requires that the lostdata be re-transmitted. To a customer of the ATM network, lost databecause of automatic path optimization can appear to be a network fault.Having to needlessly re-transmit data that is needlessly lost because ofautomatic optimization can frustrate the customers of the ATM networkservice provider.

A method for controlling automatic optimization of circuits through ATMswitches and networks might reduce needless data loss and actuallyimprove customer satisfaction by reducing the number of times that adata stream is interrupted and thereby reduce the data lost that almostalways accompanies a circuit or network optimization.

SUMMARY OF THE INVENTION

In an ATM switching network made up of several ATM switches throughwhich PVCs are established, many ATM switches are programmed toautomatically re-configure or re-define a PVC periodically so as tomaximize system capacity or to balance the data loading on the switchesand their associated links. As most ATM switches are currently designed,re-configuring a PVC in an ATM network requires that a data streamrouted over one or more data links and through one or more switches bechanged to run through one or more different switches in order to routethe data over different links. Even when a data path switch is performedautomatically, changing a data path over which a data stream is carriedalmost always causes a data loss, requiring data retransmission. In manyinstances it might be preferable to refrain from automaticallyre-optimizing a PVC path.

Data loss due to automatic network optimization can be minimized whilemaintaining network optimization by tracking the history ofoptimizations done on a customer's data stream and inhibiting subsequentautomatic optimizations until some event has occurred. Briefly themethod includes: a) tracking the history of path optimization for atleast one particular data stream through a network, includingidentifying the PVC or data path through the network for that particulardata stream at least some period of time; b) recording the occurrence ofat least the most recent automatic PVC re-configuration for the datastream; c) inhibiting any subsequent (or second) automaticre-configurations of the PVC carrying the data stream through said ATMnetwork until after the occurrence of some predetermined event, such asthe passage of some length of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified block diagram of an ATM switching network.

FIG. 2 shows a simplified block diagram of an ATM switch that might beused in an ATM switching network, such as that shown in FIG. 1,including a software controlled switch matrix or fabric that isautomatically periodically re-configured.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a simplified block diagram of an ATM switching network(100) comprised of several ATM switches (106, 108, 110, 112 and 114).The switches (106, 108, 110, 112 and 114) can route data from a source(102) to a destination (104) over several data conduits or physicalmedia (120, 122, 124, 126, 128, 130 and 132) that operatively link thevarious switches together to form the network (100). The physicalcharacteristics of data conduits (120, 122, 124, 126, 128, 130 and 132)are not germane to the invention but for completeness, those skilled inthe art will recognize that they might be optical fiber, coaxial cable,microwave link or copper wires. While there is shown in FIG. 1 only oneconduit between any two switches, actual embodiments of ATM networkstypically provide several conduits between the switches so as toincrease data capacity of the network (100).

A permanent virtual circuit or PVC is generally considered by thoseskilled in the art to be comprised of a subset of the switches (106,108, 110, 112 and 114) pre-programmed to establish a relativelylong-lived data path through the network (100) from the source (102) tothe destination (104) over some subset of the several data conduits. APVC is established by programming various switches to establish avirtual circuit through the network that remains in place through thenetwork for at least the duration of a call or data transfer. Switchedvirtual circuits, or SVCs, are data paths that are more short-livedconnections than PVCs. SVCs are frequently changed during the course ofa data transaction.

Most ATM network providers monitor the traffic loading through thenetwork in an effort to maximize data throughput and networkreliability. If for example one conduit (124) being used to route datafrom a source ATM switch (106) to a destination ATM switch (114) becomesover-loaded, fails, or is suspected of being faulty, ATM switchingsystem software in the ATM switching systems (106, 110) will frequentlyre-configure the network (100) in an effort to maintain systemthroughput and reliability. The ATM network is automatically optimizedunder software control. Re-configuring or optimizing the network (100)might entail re-routing data from path 124 onto path 122 for example.

Whenever a PVC through an ATM network is “optimized” data mayoccasionally become lost when the data being carried from the source(102) to the destination (104) is re-routed from one PVC to another.Notwithstanding the speed at which new-technology switches can bereconfigured, there are many technical reasons why at least some data ofan ATM network customer may become lost due to the re-routing of fromone PVC to another. When data is lost during the course of an ATM PVCre-configuration, the data transmission equipment of the customer willdetect an error and will almost always resend the data.

Automatic re-optimization of data paths should be controlled to avoiddata loss if data path re-configuration becomes the source of excessivedata losses. Controlling automatic data path optimization can actuallyimprove customer satisfaction without adversely affecting systemreliability.

FIG. 2 shows a simplified block diagram of a single ATM switch (200)that might be used in the ATM network shown in FIG. 1. In FIG. 2, an ATMswitch controller (210) (typically a programmable computer) executesinstructions stored in a memory device (240) (RAM, ROM, EEPROM, on diskor equivalent storage device) and records operating data elsewhere inmemory (250). The instructions and data are transferred to and from theprocessor (210) over an appropriate bus (260).

Program instructions for the controller (210) will typically cause thecontroller (210) to monitor the status of the ATM switching equipment(230) that accomplishes the ATM switching function of data transferredvia the ATM links 232, 234 that is required to make the switchingnetwork (100) of FIG. 1 operative. Data loss attributable to networkand/or ATM link optimization and re-configuration can be avoided bylimiting automatic ATM network optimization using the methodology of theinvention disclosed hereinafter.

If the ATM switch controller (210) detects that one or more data streamsrouted from a link input (232) to a link output (234) to the switch isscheduled to be optimized, the controller (210) first determines whetheror not an optimization should in fact be made, prior to executing theoptimization task. The ATM controller (210) records the occurrences ofautomatic re-configurations and uses those records to determine ifsubsequent automatic re-configurations should occur or if they should beinhibited. If a link has been recently optimized, subsequentre-optimization is inhibited unless certain conditions are met. Statedalternatively, automatic optimization can be inhibited until theoccurrence of some other event, such as the passage of some minimumlength of time since the last optimization was performed. Other eventswhich might be checked prior to automatic optimization include, but arenot limited to, the addition or deletion of any other data path orconduit through the network (120, 122, 124, 126, 128, 130 and 132); theaddition or deletion of an ATM switch to the network; the detection orcorrection of a fault on a data conduit or in a switch. In oneembodiment of the invention, a switch (and/or its associated controller210) through which data is passing controls the execution of theautomatic re-configuration for network optimization.

In some instances, an inhibited network optimization might not beappropriate, such as when a switch or media (120, 122, 124, 126, 128,130 and 132) fails. In such cases, a network might require optimization.In another embodiment of the invention, an ATM network service providercan manually invoke the execution of the automatic optimization softwarefor the controller (210) from a maintenance terminal or input port tothe controller (210) (not shown) in order to effect a networkoptimization.

By controlling automatic network optimization, which is a common featurein software controlled ATM switches and ATM networks, customersatisfaction can be improved by reducing needless data loss that isattributable to the pre-programmed and untimely network reconfigurationsthat are done without considering the impact that reconfiguration mighthave on customer data.

What is claimed is:
 1. In an ATM network comprised of a plurality of ATM data routes through one or more ATM switches through which one or more PVCs can be established to route data between end points, said PVCs being automatically re-configured to optimize data flow through said ATM data routes, a method of controlling data loss to a data stream attributable to automatic re-configuration of said PVCs comprising: a) identifying a PVC for a data stream at a first period of time; b) recording the occurrence of an automatic PVC re-configuration for said data stream through said ATM network; and c) inhibiting a second automatic re-configuration of said PVC through said ATM network until after the occurrence of a predetermined event, wherein said predetermined event is the addition of at least one additional ATM data route through a switch of said ATM network through which said data stream passes.
 2. The method of claim 1, wherein said second automatic re-configuration of said PVC through said ATM network, is controlled by said at least one additional ATM switch. 